Production of lubricating oils

ABSTRACT

LUBRICATING OILS OF IMPROVED VISCOSITY INDEX AND IMPROVED STABILITY TO ULTRAVIOLET LIGHT ARE PREPARED BY A PROCEDURE INVOLVING HYDROCRACKING, SOLVENT EXTRACTION, HYDRGENATION OF THE AROMATIC-RICH EXTRACT AND REBLENDING.

United States Patent O U.S. Cl. 208-58 9 Claims ABSTRACT OF THE DISCLOSURE Lubricating oils of improved viscosity index and improved stability to ultraviolet light are prepared by a procedure involving hydrocracking, solvent extraction, hydrogenation of the aromatic-rich extract and reblending.

This invention relates to the production of lubricating oils. More particularly it is concerned with the conversion of low quality lubricating oil stocks into lubricating oils of high viscosity index in good yields.

It has been customary in the past to increase the viscosity index of lubricating oils, particularly crankcase oils by the addition thereto of viscosity index improvers. The high viscosity index oils so produced were then satisfactory for use in automobile engines. However, increased demands for wide temperature range automatic transmission fluids and wider range multigrade motor oils such as W-30 and 10W-40 which normally would require increased amounts of viscosity index improvers have created a greater need for higher V.I. base oils to minimize the quantity of V.I. improver used and thus improve shear stability. Thus, there is now a great need for lubricating base oils which have a high viscosity index. While this may not be too difiicult when high quality lubricating oil stocks such as Pennsylvania oils are used as a starting material, there are not sufficient oils of such high quality to meet the greatly increased demand for high viscosity index lubricating oils of the lower viscosity grades such as SAE 10 and SAE 20 grades and it is now becoming necessary not only to start with low grade lubricating oil stocks, that is, stocks having a. viscosity index of less than 80 or even less than 75 but also to effect a V.I. improvement Without suffering a substantial loss in yield.

Various processes are available for the refining of lubricating oil charge stocks. conventionally, the lube oil stock obtained either by vacuum distillation or by deasphalting a vacuum residuum can be improved by solvent extraction to increase the viscosity index and by solvent dewaxing to lower the pour point. Acid treating may be used to improve the color, the stability and the resistance of the oil to oxidation and clay contacting is used to further improve the color and to neutralize the oil after acid treatment. More recently severe catalytic hydrogenation of the oil has been proposed as a substitute for solvent refining to increase the viscosity index of the oil. However, the resulting product oil is not stable towards ultraviolet light and with certain feedstocks, relatively low yields are obtained.

It is an object of this invention to produce lubricating oils of improved viscosity index from low-quality lubricating oil charge stocks. Another object is to produce lubricating oils of high viscosity index from low quality charge stocks in yields not obtainable by the processes of the prior art. Still another object is to produce lubricating oils which are stable to ultraviolet light. These and other objects will be obvious to those skilled in the art from the following disclosure.

According to our invention, there is provided a process for the production of lubricating oils which comprises subjecting a lubricating oil charge stock to hydrocracking to reduce its average molecular weight and to convert a substantial portion of the aromatic compounds present to more saturated compounds. The hydrocracking zone eflluent is fractionated to recover a lube oil cut which is solvent refined to produce a raflinate rich in parafiins and naphthenes and an extract rich in aromatics. The extract is contacted with a hydrogenation catalyst under hydrogenation conditions and at least a portion of tho hydrogenated extract is combined with the raffinate 01' recycled to the solvent refining step.

Examples of the lubricating oil charge stock contemplated by our processes are petroleum fractions having a viscosity between 50 and 500 SUS at 210 F. Although the invention is applicable to any lubricating oil charge stock, it is particularly suitable for the treatment of medium-quality charge stocks, that is, those charge stocks having a viscosity index not greater than about and more particularly for the treatment of low-quality charge stocks, that is, those having a viscosity index below about 80 to produce improved lubricating oils having a viscosity index at least 20 units higher than that of the charge stock.

Lubricating oil stocks are ordinarily obtained by distillation of crude petroleum. The stock may be obtained as overhead from a vacuum distillation or may be obtained from the residue of a vacuum distillation by deasphalting the residue by contact with, for example, a deasphalting agent such as propane, butane and the like and mixtures thereof.

The lube oil stock is then subjected to catalytic hydrocracking by, in a preferred embodiment, passing the oil and hydrogen downwardly through a fixed bed of particulate catalyst at a temperature between about 700 and 900 F., a pressure bet-ween about 800 and 5000 p.s.i.g., a space velocity of about 0.1 to 5.0 volumes of oil per volume of catalyst per hour with a hydrogen rate of between about 1500 and 20,000 standard cubic feet per barrel of charge. Preferably, the temperature is maintained within the range of 725-850" F., the pressure between 1300 and 3,000 p.s.i.g., the space velocity between 0.15 and 1.5 v./v./hr. and the hydrogen rate between 3,000 and 10,000 sc.f.-b. The gas used for the hydrogenation need not necessarily be pure hydrogen. Hydrogen having a purity of at least 65 percent and preferably a purity of 75 to percent may be used.

The catalyst used in the hydrocracking step generally comprises a hydrogenating component carried on a support. The principal ingredient of the hydrogenating component is a Group VIII metal or mixtures of Group VIII metals or compounds thereof. Examples of Group VIII metals which may be used in the hydrogenating components are nickel, cobalt and iron or compounds thereof, such as the oxides or sulfides. The iron group metal should be present in an amount between about 2 and 40 percent, preferably 2-15 percent, based on the total weight of the catalyst composite. In conjunction with the iron group metal, a Group VI metal such as molybdenum or tungsten may be used. In such case the Group VI metal may be present in an amount between about 5 and 40 percent based on the weight of the composite, a preferred range being from 10 to 25 percent.

The hydrogenating component may be carried on a support comprising a refractory inorganic oxide material such as alumina, silica, magnesia, zirconia, titania, crystalline alumino silicates and the like and mixtures thereof. When the lubricating oil stock introduced into the hydrocracking zone is derived from a deasphalted residuum and it is desired to convert the extract into a lubricating oil of the SAE 10 or SAE 20 grade then advantageously the catalyst has an acidic support such as a crystalline alumino silicate of the zeolite Y type of reduced alkali metal content, e.g., less than 1.0 weight percent composited with a mixture of an amorphous inorganic oxide material such as 70-90 percent silica and 10-30 percent alumina. If the extract has been obtained from a wax distillate, then advantageously the catalyst support may have reduced cracking activity or the hydrocracking may be carried out under milder conditions. When it is desired to suppress the cracking activity of the catalyst, a small amount of ammonia or carbon monoxide may be introduced into the reaction zone. A suitable amount depending on the extent to which the cracking is to be reduced will range between about 0.1 and 2.0 percent ammonia or carbon monoxide based by weight on the oil charge.

The catalyst may be used in the form of a slurry, a fluidized bed or a fixed bed. When used in the form of a fixed bed, the oil and hydrogen flow may be either upward or downward or the flow of hydrogen may be countercurrent to the downward flow of oil. Suitable catalysts are those containing from 2 to 10 percent cobalt or nickel and 8 to 30 percent molybdenum or tungsten. Particularly suitable catalysts are those containing about 6 percent nickel and 20 percent tungsten or about percent nickel or cobalt and about -15 percent molybdenum on alumina containing 2-15% silica.

After separation of the lower boiling components from the hydrocracking zone eifiuent, the hydrocracked lube oil fraction is subjected to solvent extraction using a solvent having an affinity for aromatic hydrocarbons. Particularly suitable solvents include furfural, phenol, dichloroethyl ether and N-methyl-2-pyrrolidone. Advantageously, the extraction is carried out using a countercurrent flow technique, the solvent being introduced at the top of an extraction tower and the oil near the bottom with the tower being maintained at a temperature between about 150 and 250 F. The solvent to oil ratio may range between about 1 to 6 by volume. Oil is recovered from the top of the tower as raffinate and is advantageously further processed by heating and steam stripping to remove residual solvent. Solvent and extract are removed from the bottom of the extraction tower and are separated by distillation.

The extract is then subjected to catalytic hydrogenation under relatively mild conditions including a temperature of 525-725 F., a pressure of 300-1800 p.s.i.g., a p.s.i.g., and a space velocity between 0.25 and 3 v./v./hr. in the presence of hydrogen introduced at a rate of from 100-3000 s.c.f.b. Preferred conditions include a temperature of 525-725 F., a pressure of 300-1800" p.s.i.g., a space velocity between 0.5 and 1.5 and a hydrogen rate between 1000 and 5000 s.c.f.b. The conditions are selected within the above ranges so that there is substantially no conversion to materials boiling below the lube oil range. Ordinarily the product lube oil yield from the hydrogenation step is not less than about 95 volume percent basis charge to the hydrogenation zone.

Suitable hydrogenation catalysts comprise metals or compounds of metals of Group VI and Group VIII of the Periodic Table. Non-limiting examples of such components are chromium, molybdenum, tungsten, iron, cobalt and nickel and compounds thereof or their mixtures. Generally these components are supported on a base comprising a refractory inorganic oxide material such as alumina, silica, magnesia, zirconia, titania and the like and mixtures thereof. The support should not have cracking activity. The catalyst may be used in the form of a slurry, a fixed bed, or a fluidized bed. When used in the form of a fixed bed, the flow may be either upward or downward or the flow of hydrogen may be countercurrent to the flow of oil. Particularly suitable catalysts are those containing from 2-10 percent coablt or nickel or 5-30 percent molybdenum or tungsten. Preferred catalysts are those containing about 6 percent nickel and percent tungsten or about 2-4 percent cobalt or nickel and 5-10 percent molybdenum supported on alumina. Although the catalyst may be subjected to chemical change in the reaction zone due to the re ence of sulfur and hydrogen therein, the

catalyst is ordinarily in the form of the oxide or sulfide when first brought into contact with the charge stock.

The hydrogen used in the hydrogenation step as in the hydrocracking step need not be pure hydrogen. Satisfactory results may be obtained with hydrogen containing as much as 30-40 percent impurities. Suitable sources of hydrogen are catalytic reformer by-product hydrogen and hydrogen produced by the partial combustion of a hydrocarbon material followed by shift conversion and scrubbing. The hydrogen for the hydrocracking and the hydrogenation may come from a common source or each may have its own system.

To improve its pour point, the oil is contacted with a dewaxing agent such as a mixture or equal parts of a ketone, for example, acetone or methylethyl ketone and an aromatic compound such as benzene or toluene, in a ratio of about 3 to 4 parts by volume of solvent per volume of oil. The mixture is cooled to a temperature of about 0 to -20 F. depending upon the desired pour point and the waxy components are removed from the chilled mixture by filtering or by centrifuging. The de- Waxing may precede the hydrocracking or may be performed separately on the rafiinate and the hydrogenated extract or the ralfinate and the hydrogenated extract may be combined and then dewaxed. In any event, the hydrogenated extract and the raffinate are combined to produce the product oil.

The example below is presented for illustrative purposes only and it is not to be construed that the invention is restricted thereto.

EXAMPLE In this example the charge is a dewaxed oil having an API gravity of 22.6 and a pour point of 0 F. Other characteristics appear below in Table I. Data on the catalyst used in the hydrocracking stage and reaction conditions are as follows:

hydrocracked lube oil product is extracted with furfural using two treatments at dosage at a temperature of F. and separated into a rafiinate phase and an extract phase. After removal of the furfural, the extract is hydrogenated using a sulfided catalyst having the specifications and at the reaction conditions tabulated below:

TABLE II Ni wt. percent 5.9 W 18.3 Alumina Balance Surface area m. /g 171 Temperature F 700 Pressure p s i 1800 Space velocity v./v./hr 0.5 Hydrogen rate s.c.f.b 5000 After flashing the gaseous material from the hydrogenation efiluent, the lube oil fraction is combined with the raffinate from the solvent extraction step. Yield figures and other data are tabulated below:

It will be noted that an increase in yield of better than 30% is obtained while sustaining an insignificant loss in the viscosity index of the product. It will also be noted that although the viscosity index of the hydrogenated extract is just 34, only a small loss in viscosity index from that of the raifinate is sustained by the blending.

The product blend also shows good stability towards ultraviolet light.

Obviously, various modifications of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be made as are indicated in the appended claims.

We claim:

1. A process for the production of a lubricating oil of improved viscosity index which comprises contacting a lubricating oil fraction selected from the group consisting of petroleum distillates and deasphalted residua with hydrogen under hydrocracking conditions including a temperature between 700 and 900 F. and a pressure between about 800 and 5000 p.s.i.g. in the presence of a hydrocracking catalyst, recovering from the hydrocracking zone efiiuent a hydrocracked fraction boiling in the lubricating oil range, subjected said hydrocracked lubricating oil fraction to solvent extraction with a solvent having affinity for aromatic compounds to produce an aromatic-rich extract and an aromatic-poor raflinate, hydrogenating said extract by contacting same with hydrogen in the presence of a hydrogenation catalyst at a temperature between about 450 and 750 F. and a pressure between about 250 and 1000 p.s.i.g. and combining the hydrogenated extract with said raffinate.

2. The process of claim 1 in which the feed lubricating oil fraction is a petroleum distillate.

3. The process of claim 1 in which the feed lubricating oil fraction is a deasphalted residuum.

4. The process of claim 1 in which the hydrocracking is conducted at a temperature between 725 and 850 F. and the hydrogenation is conducted at a temperature between 525 and 725 F.

5. The process of claim 1 in which the yield of lube oil in the hydrogenated extract is not less than basis charge to the hydrogenation zone.

6. The process of claim 1 in which the feed to the hydrocracking zone is a dewaxed petroleum distillate.

7. The process of claim 1 in which the solvent is furfural.

8. The process of claim 1 in which the solvent is N- methyl-Z-pyrrolidone.

9. The process of claim 1 in which the combined raflinate and hydrogenated extract is subjected to a dewaxing treatment.

References Cited UNITED STATES PATENTS 2,967,146 l/196l Manley 20818 3,256,175 6/1966 Kozlowski et al. 208 58 3,365,390 1/1968 Egan et al. 20818 3,652,448 3/1972 Cummins 208--18 HERBERT LEVINE, Primary Examiner US. Cl. X.R. 20858, 96

v UNITED STATES PATENT; CERTIFICATE OF CORREQTION Patent No. 5,790,470 Date'd ebr ry ,1974

Invenunis) Theodore C. Mead et a1;

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

same line 43, "of 3001800" Should read---dbeiween 250 and 1000 Column 5, line 37, "subjected" shopld readsubjecting Signed and sealed this 22nd day o*o; '1914.

(SEAL) Attest:

MCCOY M. GIBSON JR. CQ-MARSHALL DAEN Attestlng Officer- Commissiqper of Patents Column 3, line 43, "525 72s F." should read -s-4s0 7s0 F.

ORM PO-lOSO (O-69) USCQMM'DC 603764 89 us cuvlzmmzm PRINTING omcz; 93 o 

